The present invention relates to a method of efficiently and economically producing pentafluorophenylmagnesium derivatives using pentafluorobenzene as a raw material. The pentafluorophenylmagnesium derivatives are very useful raw materials for pentafluorophenylation and used as important reactants when producing various intermediates for medicinal drugs or boron derivatives which are very useful as cocatalysts for cationic complex polymerization, for example, tris(pentafluorophenyl)borane and tetrakis(pentafluorophenyl)borate derivatives by reacting them with boron compounds such as boron trifluoride or boron trichloride.
In the conventional production method of pentafluorophenylmagnesium derivatives, very expensive pentafluorobromobenzene is generally used as a starting material for the source of pentafluorophenyl group. For example, there are J. Chem. Soc., 166 (1959), Z. Naturforschg., 20b, 5 (1965), Synthesis of Fluoroorganic Compounds, p. 141, Springer-Veriag (1985), etc. Moreover, in the production method using pentafluorobenzene as a starting material for the source of pentafluorophenyl group when producing pentafluorophenylmagnesium derivatives, it is reported that pentafluorophenylmagnesium derivatives can be obtained in a yield of 86% by using tetrahydrofuran as a reaction solvent and reacting for 5 hours at room temperature (J. Org. Chem., 29, 2385 (1964)).
In the conventional production method using pentafluorobenzene as a starting material for the source of pentafluorophenyl group, tetrahydrofuran is used as a reaction solvent. However, in a reaction system such that strong Lewis acids such as titanium tetrachloride, boron trichloride, boron trifluoride and tin tetrachloride coexist, tetrahydrofuran ends up to polymerize, hence a production method in other reaction solvent system difficult in polymerization has been required. Moreover, while pentafluorobromobenzene being a starting material for the source of pentafluorophenyl group is very expensive, pentafluorobenzene is also relatively expensive, hence, the improved yield has been desired also in the production method using pentafluorobenzene as a starting material and tetrahydrofuran as a reaction sovlent.
In view of said situation, the inventors investigated extensively on a process which has a versatility as a production method of pentafluorophenylmagnesium derivatives using pentafluorobenzene as a starting material, in which the yield is quantitative and the application scope is broad, and which is more economical not requiring a temperature as very low as -70.degree. C. on production over pentafluorophenyllithium used for the similar reaction, leading to the invention.